The present invention relates to building panels for use in construction, and, in particular, to a composite, light-weight building panel for use as an exterior curtain wall panel in commercial exterior finish and insulation systems.
Exterior finish and insulation systems ("EFIS") for exterior walls have become increasingly popular in commercial construction as alternatives to brick, stone, metal, and wood facades. The EFIS system is characterized by a foam facing, expanded polystyrene or polyurethane, which is adhered to a support substrate. The foam facing is covered by a base coat of synthetic plaster and portland cement in which a fiberglass mesh is embedded. The base coat is covered by a finish coat of synthetic plaster. The finish coat may be applied with different textures in almost unlimited colors to provide a wide variety of aesthetic appearances.
EFIS wall systems may be constructed on-site or manufactured as panels which are brought to the site as completed components and attached to the building support structure. The most common type of panel using the EFIS systems uses a steel stud and gypsum framing wall as the substrate for mounting the foam facing. More particularly, a series of uniforms spaced metal studs are connected to metal channels at the top and bottom. Gypsum sheathing is attached to the studs by conventional fasteners. The foam facing is then adhered to the sheathing by adhesives and finished as described above.
The EFIS panel may incorporate additional batt insulation between the studs and the interior finished with dry wall or the like. These panels are less expensive than other facades, result in lower construction, installation and maintenance costs, and can reduce energy consumption. However, such panels have certain disadvantageous. Although lighter than solid stone panels and like facades, these panels are quite heavy. In large sizes the weight of the panel requires lifting devices such as cranes for hoisting the panel to the desired location on the building. Moreover, the insulating value of the panels is generally only R6-R8 unless batt insulation is installed between the studs which then provides and overall R-value of about 20. However, batt insulation is prone to sagging with an inconsistent insulating value over time. Perhaps, the biggest limitation of these panels is delamination of the foam and coatings at the foam-gypsum interface. This can readily occur where moisture is able to penetrate the sheathing and over time loosen the bond between the gypsum and foam deteriorates. As a result, there can be peeling of the coated foam or complete separation from the support frame.
To overcome the above delamination problems, another approach has utilized a large foam panel having vertical grooves into which opposed pairs of rectangular tubes were adhesively connected. The tubes are connected at the top and bottom to horizontal channels by fasteners. Because the base coat does not adhere tenaciously to steel, the tubes are covered by thin strips of foam. This can present problems in finishing the panel in that the strip must be level with the front coating surface to avoid seeing the strips after the coating is applied. This can require considerable finishing labor, primarily sanding or rasping of the surface to insure that all surfaces are level. Moreover, these strips must be securely attached to avoid possible delamination, but however form a lesser difficulty than the gypsum/foam delamination referred to above.